An investigation into a mishap involving a Qantas flight last month is centring on an electronic black box which produced spurious message signals causing the aircraft to dive suddenly.
There was also a possibility the incident was caused externally by signals from a naval communications base near Exmouth in Western Australia, the Australian Transport Safety Bureau said today.
Forty-four of the 313 people on board required hospital treatment after the Qantas Airbus A330, flying from Singapore to Perth on October 7, suddenly plunged, hurling passengers around the cabin.
The aircraft was cruising at 37,000 feet when the fault occurred, causing it to descend up to 650 feet in seconds.
The pilot made an emergency landing at Learmonth in north-western WA.
An initial investigation pointed to a fault in the plane's air data inertial reference system which sent erroneous information to the flight control computer, causing the autopilot to shut down.
The bureau today released a preliminary report of its inquiry, saying the electronic black box - known as ADIRU (Air Data Inertial Reference Unit) - was normally highly reliable.
It was extremely rare for such failures to have an effect on an aircraft's flight control, inquiry official Kerryn Macaulay told reporters in Canberra.
"The three ADIRUs will be subject to comprehensive testing at the manufacturer's facility in the US,'' she said.
Testing is planned to start on Monday.
The bureau's investigation is also considering the possibility the incident was caused by external interference, possibly by signals from the Navy's Harold E Holt submarine's communications base.